It is not obligatory to supplement an html campaign with a plain text version of it; however, it is good practice in terms of email deliverability. There are several explanations for this:
- Spam filters prefer to see the alternative plain-text version of the html email in order to let it through to people’s inboxes. This function of spam filters can be easily explained by the fact that spammers usually do not take the time to create the plain-text versions. If you take time to do it, you will be rewarded with more successful automated campaigns.
- Some email clients or applications do not support the html format. This can result in non-deliverability of your emails to such subscribers. Having a plain-text backup version will ensure that the subscribers will see your email. There will be no images or rich formatting, but the main point of it – the information and URLs – are going to be preserved.
If you do not include the plain-text alternative, for the abovementioned reasons your subscribers are likely to see this: